1. Field of the Invention
The present invention relates to a semiconductor device which can seat a high-frequency semiconductor integrated circuit and the like at a high density and electronic equipment using such a semiconductor device.
2. Background Art
Portable electronic equipment such as a mobile telephone is equipped with diversifying functions, e.g., the equipment comprises a display of a large size so as to display images, pictures and the like, the equipment incorporates a memory card, etc. A concurrent and major shift on mobile telephones is that most of them are of the folding type. In this circumstance, a printed board needs be thinner when mounted inside. To add to the difficulty, a large-size display, a key board and the like on one surface of the printed board make it increasingly hard to mount other components on this surface of the printed board.
In connection with a high-frequency semiconductor integrated circuit used in a mobile telephone, a package of the QFP type is advantageous in requiring only fewer pins which helps size reduction, and this type of package has an improvement that the back surface of the package comprises a common plate for grounding. FIG. 10 shows a structure which uses a package of the QFP type. In FIG. 10, denoted at 1071 is a semiconductor integrated circuit chip sealed in QFP, denoted at 1072 are terminals of QFP, denoted at 1073 is a grounding plate of QFP, denoted at 1074 is a multi-layer mounting board, denoted at 1075 is a front-layer grounding pattern, denoted at 1076 are peripheral circuit components, and denoted at 1077 are through holes. As shown in FIG. 10, while the semiconductor integrated circuit chip 1071 of QFP is mounted within a chip mounting area 1071A on the front layer of the board 1074, since the grounding pattern 1075 needs be disposed on the front layer of the board 1074 in an area which corresponds to the grounding plate 1073 of the chip 1071, signal wires must be all led out from outside the pins (terminals 1072). This necessitates a void space where no component can be mounted, which is a disadvantage that the mounting area increases.
Noting this, among endeavors to reduce the size of a package, some high-frequency semiconductor integrated circuits for use in mobile telephone have started to use a chip size package (CSP) of the ball grid array (BGA) type instead of a package of the QFP type, for the purpose of reducing the mounting area. A package of this type achieves a small mounting area, as external peripheral components are mounted on the both surfaces of a mounting board as shown in FIG. 8. In FIG. 8, denoted at 861 is a semiconductor integrated circuit chip, denoted at 862 is a multi-layer mounting board, denoted at 863 are peripheral circuit components to be mounted on a front layer, and denoted at 864 are peripheral circuit components to be mounted on a back layer. With the peripheral circuit components 864 mounted on the back side of the mounting surface of the semiconductor integrated circuit 861 within the back layer, it is possible to realize mounting that the wires are short and less intersect with other wires (See Japanese Patent Application Laid-Open Gazette No. 2003-204163 and Japanese Patent Gazette No. 3507300.)
However, even in the case of a CSP of the BGA type described above, it is becoming difficult to mount other components on one surface as explained earlier. Owing to this, as shown in FIG. 9, where a key board 966 is disposed on the back surface and mounting on the both surfaces is therefore impossible, it is necessary to mount the components 965, which used to be mounted on the back surface (and which correspond to 864 shown in FIG. 8), to wires which have been pulled up to the front layer using interconnections, through holes, etc. This complicates signal wires, leading to inconveniences and problems such as crosstalk.